Method op maintaining electric currents op constant frequency



March 26, 1929. I w. G. CADY Re. 17,246

METHOD OF MAINTAINING ELECTRIC CURRENTS 0F CONSTANT FREQUENCY Original Filed May 28, 1921 Arroe/vir Reissued Mar. 26, 1929.

UNITED STATES PATENT OFFICE.

WALTER G. CADY,'0F MIDDLETOWN, CONNECTICUT, ASSIGNOR T RADIO CORPORA- TI ON OF AMERICA, A COBYORATION OF DELAWARE.

, MnrHon or marngrnnme ntno'rnrc CURBENTS OF CONSTANT FREQUENCY.

a1 110.4%,434, filed May 28, 1921. Application for I reissue filed August 6, 1925. Serial No. 48,682.

DIVISION B The invention which forms the subject of my present application for Letters Patent is an improvement in the art of producing and maintaining alternating currents of Constant 5 frequency. It is well known that, heretofore, the development of such currents, to-- any very high degree of precision, has been unattainable by ordinary means and great difiioulty has been experienced in producing alternating currents of high and constant frequency and free from fluctuations, due to disturbances in or near the generating system.

The useful applications of my invention are numerous. It may be employed in the trans- 5 mission or the reception of'intelligence by means of high-frequency currents, or it may be used for the testing and measurement of such currents, in all cases where the frequency can be varied, and, in general, the invention is applicable to currents of any frequency.

In an application filed by me on January 28, 1920, Serial'No. 354,659, which has matured into Patent No. 1,450,246, April 3, 1923, I have shown and described what I have termed a piezo-electric resonator, which, in general, comprises a plate of piezo-electric crystal with coatings on its opposite faces. The coatings maybe either thin layers of metal on the crystal itself, or metallic plates in fixed relation to the crystal, or, in general, any means whereby an electric charge may be conducted to the resonator in such a way as to produce an electric field in the proper direction through the crystal. Such a device has a natural period of vibration, but when set in vibration by a source of alternating current connected to its coatings, the amplitude of such vibrations is very slight, unless the frequency of the alternating current approximates or equals'the natural frequency" current, into another circuit; second, that property which it possesses of modifying, by

its reactions, the alternating current of aparticular frequency or frequencies flowing to it. Inthe description and explanations of my Invention which follow, I have assumed the plezo-electric resonator to comprise a single, suitably prepared plate cut from a piezoelectrlc crystal, and provided with conductive coatings, and utilizing the so-called transverse elfect; but all statements made apply equally to crystal preparations utilizing the longitudinal effect, and, in general, to any mechanical vibrating system whatever, having suitable preparations of piezo-electric crystals for setting the system into vibration and for utilizing its reactions.

The nature and purpose of the present invention may be most readily comprehended by reference to the single figure of the ac companying drawings, which is a diagram of a three-stage amplification systemof wellknown type, in which a piezo-electric resonator is employed to maintain constant frequency in accordance with my invention.

In accordance with theprinciple of operation set forth in my application, Serial No. 21,734, filed April 8, 1925, for reissue of my Letters Patent No. 1,472.583, of which the present application is a division, the piezoelectric resonator may be used with any. generator of alternating current, such as a vacuum tube, the frequency of which is capable of being determined by the varying potential dilference between two fixed points in the circuit or system of circuits.

The greater the amplification constant of the vacuum tube, the more widely may the electrical constants of the circuit be altered, without affecting the frequency. For this reason, a still greater degree of stability may be attained by the use of a plurality of tubes, connected for cascade amplification. I have found, for instance, that by the use of a cascade amplifier comprising three tubes, the coils and the tuning condenser of the wellknown and universally recognized Armstrong oscillating circuit may be entirely dispensed with.

- This arrangement of circuits is shown in the accompanying drawing, in which 4 represents the grid of the first tube and 5 the anode of the third. Two resistances 17 and 18 are employed, and two condensers 19 and 20. This illustrates the well known resistance amplification, but any other type of amplifier might be employed. In this figure, 21 is a resistance or other impedance in the anode or output circuit, while the piezo-electric resonator 12 has its two coatings 14 and 13 connected to the plate 5, and the ground 22, respectively, and its two coatings and 16 connected, the one to the ground 22, and the other to the grid 4.

The operation of this arrangement is as follows: Any slight increase in the potential of' the anode 5, by altering the electric field between the plates 13 and 14, sets the piezo-electric resonator in vibration. Thev charges thereby excited in the coatings 15 and 16 vary the potential of the grid 4: with respect to the ground 22. This varying potential, by virtue of the amplification taking place in the system, will, if the proper coating 'is connected with the grid 1,still further increasethe variations in the potential of the anode 5 and maintain the piezo-electric resonator in vibration.

From the resistance or impedance 21, a small amount of output power, at a constant frequency, may be drawn.

aving now described my invention, what I claim is: u

, 1. An oscillating system comprising a plurality of vacuum tubes having an input circuit and an output circuit, the system beingnormally non-oscillating, and an electro-mechanical vibrator coupling the circuits together and adapted together with the circuits toproduce oscillations, the vibrator being adapted to vibrate mechanically when stimulated electrically and to respond electrically when vibrated mechanically and being designed to maintain the frequency of the oscillations substantially constant.v

2. An'oscillating system comprising a plurality of vacuum tubes having an input circuit and an output circuit, the system being necting one of the grids with one of the plates and a aptedtogether with the tubes to produce oscillations, the body being designed to maintain the frequency of the oscillations substantially constant and being so connected that variations in the'potential of the said one plate will be transmitted through the body to the said one grid and from the grid back to the plate, whereby the system is rendered oscillating and at substantially constant frequency.

4. An oscillatory system comprising a plurality of vacuum tubes connected in cascade, and each comprlsing a filament, a grid and a plate, an electro-mechanical vibrator connecting the grid of one tube with the plate of another tube, the vibrator being adapted to vibrate mechanically when stimulated elect-rically and to respond electrically when vibrated mechanically.

5. An oscillating system comprising a plurality of vacuum tubes each having a filament, a grid and a plate, the system being normally non-oscillating, and a piezo-electric body connectin'g one of the grids with one of the filaments and adapted together with the tubes to produce oscillations, the body being designed to maintain the frequency of the oscillations substantially constant and being so connected that variations in the potential of the said one plate will be transmitted through the body to the said one rid and from the grid back to the plate, whereby the system is rendered oscillating and at substantially constant frequency.

In testimony whereof, I hereunto afiix my signature.

WALTER G. CADY. 

